All you need to do is visit the site you want to edit, paste the code below into your web browser address bar (tested in Firefox & IE7) and hit the Enter button. Then simply select a portion of text on the page and start editing. (Source: BlogStorm)
Just copy and paste that into your browser’s location bar, press enter and start editing any website! Wow, so that’s how you make fake screenshots. I am using Firefox 3, you could even drag and drop the images, resize them the way you want and and have the spell checking thingy.